(a) Field of the Invention
The present invention relates to a method of controlling upshift for an automatic transmission, and more particularly, to a control method performed in real-time in which runup occurring during an upshift operation from a second speed to a third speed is controlled.
(b) Description of the Related Art
Runup is a phenomenon in which clutches in the transmission are temporarily not engaged following an increase in engine drive power such that engine rpm and turbine rpm abruptly increase. Runup occurs frequently during power on upshifting from a second speed to a third speed.
FIG. 1 shows a waveform diagram of engine rpm Ne, turbine rpm Nt and a duty ratio in a vehicle applying a conventional method for preventing runup. In the drawing, line 1 (dotted line) indicates engine rpm Ne; line 2 (solid line) indicates turbine rpm Nt; and line 3, which increases in steps then decreases, indicates a predetermined duty ratio.
In the conventional method, to prevent runup during power on upshifting from the second speed to the third speed, a time T of a predetermined interval A starting from a shift start point and extending to where feedback control is performed is measured, and a compensation time Tc is duty is then compensated according to a comparison between a target shift time Tst and an actual shift time.
However, because the compensated duty is used also for subsequent shift operations from the second speed to the third speed, optimal prevention of runup is not obtained.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a method for controlling runup during an upshift operation from a second speed to a third speed in which compensation to prevent runup is performed in real-time.
To achieve the above object, the present invention provides a method of controlling upshift for an automatic transmission comprising the steps of performing upshifting from a second speed to a third speed if throttle opening and vehicle speed are at predetermined levels; determining if runup is occurring at the point where upshifting from the second speed to the third speed is performed, the determination of the occurrence of runup being performed based on turbine rpm, transmission output rpm and a second speed gear ratio; determining if a time rate of change in turbine rpm is less than 0 if runup is occurring; reducing a duty for a predetermined time period if the time rate of change in turbine rpm is greater than 0; and performing feedback control if the time rate of change in turbine rpm is less than 0.
According to a feature of the present invention, the step of determining if runup is occurring, it is determined that runup is occurring if turbine rpm Nt are greater than a result of adding a first predetermined value of rpm to the product of the second speed gear ratio and the transmission output rpm.
According to another feature of the present invention, the first predetermined value of rpm is 100 rpm.
According to yet another feature of the present invention, the step of determining if runup is occurring further comprises the steps of determining a point at which feedback occurs if it is determined that runup is occurring; and performing feedback control if feedback is occurring.
According to still yet another feature of the present invention, the step of determining the point at which feedback occurs is performed by determining if turbine rpm Nt are greater than a second predetermined value of rpm subtracted from the product of the second speed gear ratio and the transmission output rpm.
According to still yet another feature of the present invention, the second predetermined value of rpm is 35 rpm.